Abstract

Main objective & context: In the context of growing competition for Alpine water resources between humans and nature, small changes in percentage of water availability may give rise to intense multi-stakeholder negotiations. This research programme proposes to quantify the origin of available water resources as an essential ingredient for a more precise assessment of possible future scenarios, which is a prerequisite for sustainable water use (e.g. for hydropower production). Most available water resources projections rely on model predictions obtained using relatively poor quality observed precipitation, discharge and glacier mass balance data. To critically improve our understanding of the involved natural processes and to increase the reliability of such prediction models, an actual characterisation of the origin of observed river water (from recent precipitation or older accumulations in glaciers and permafrost) is required. Proposed research & approach: The research will address novel questions on the origin of Alpine water based on a combined experimental-modelling approach: Stable water isotope tracers in different water stores will be used as fingerprints to formulate testable hydrological hypotheses about the origin of the water and what mixing processes it has undergone. The viability of these hypotheses will be evaluated with the help of a catchment-scale model with a flexible model structure. The key hereby will be a more precise quantification of where Alpine water is stored, followed by proper accounting for dominant sources of modelling uncertainties to ensure robust conclusions on the origin of observed water resources. Approach: The core of the proposed research will be the development and application of an original, combined experimental-modelling framework. The research will be completed in 4 work packages: 1) Hypothesis formulation: Collection of existing and new tracer data to quantify the origin of water in different compartments (snow, soil, moraine, (rock-) glaciers); formulation of hypotheses about dominant hydrological processes and translation of these hypotheses into a perceptual model that can be encoded in a numerical model. 2) Modelling: Development of a catchment-scale hydrological input-output model with a flexible model structure that can predict the transport of water and tracers through the different storage compartments. Testing of how different model structures can reproduce observed data and what information is missing to properly constrain the model. 3) Uncertainty quantification: Development of a Bayesian framework to quantify the modelling uncertainties for the tracer simulation in the experimental catchment and prediction of water resources uncertainties for present and near-future situations. 4) Synthesis: Application of the Bayesian framework to quantify the uncertainties in predicting the water resources in catchments without additional observations about the origin of observed discharge and propagation of these uncertainties into plausible near-future climate and land use change scenarios.Implementation & personnel: The research will be hosted at the Institute of Earth Surface Dynamics (IDYST) of University of Lausanne. The research group will be composed of the principal investigator (PI), two PhD students (full-time 4 years) and a postdoc (full-time 4 years). At the interface of ongoing research in several groups of the host institute, the research will fully benefit from and contribute to the expertise in analysing and modelling environmental processes. Data: The research will make use of the hydro-meteorological data available in the experimental Vallon de Nant catchment of the host institute, where all additional field campaigns are also to take place. Discharge and meteorological data for other Swiss catchments are available from the Federal offices, additional isotope tracer data through (inter-)national collaborations. The research will draw benefit from the excellent measurement equipment and lab facilities at the host institute.Outcome: The outcome of this research is threefold. It will: (i) Assess, for selected high Alpine catchments, the origin of available water resources and provide a more robust assessment of their potential future evolution. (ii) Unravel potential shortcomings and related uncertainties in model-based predictions of future water resources with direct relevance for water and ecosystem management. (iii) Synthesize how isotope tracer data can reduce water resources prediction uncertainty in high Alpine environments.Innovation: The isotopic data set will be one of the largest for high Alpine environments. The modelling framework will be the first one that builds upon an explicit integration of water and isotope tracer mass balance in a single model to assess the water resources in high Alpine areas on a range of time scales relevant for water resources management (daily to annual) and including uncertainty quantification. This is both an important but also a truly unique endeavour.